A common form of corrective eye surgery is keratoplasty, the transplanting of corneal tissue from a donor to a patient with corneal problems. Advances in the field of keratoplasty have considerably increased the rate of success in these operations. However, this success rate usually relates to the attaining of a clear cornea. There remains a problem with these operations in that post-operative astigmatism following the corneal graft occurs in a large number of cases, and this can severely limit the visual acuity of the patient.
Attempts at controlling this astigmatism have largely been limited to the development of different suturing techniques. These techniques have included the use of different sized non-reactive Nylon sutures, the use of continuous running Nylon sutures, sometimes in combination with interrupted corneal sutures, and other methods. Despite all of these attempts at reducing astigmatism, the results have fallen far short of ideal. Recent studies have shown that astigmatism following suture removal has been largely unaffected by these various suturing techniques. The methods used thus far have not been successful in reducing final astigmatism following corneal transplant and suture removal.
Evidence is starting to accumulate which suggests that the major determinants of astigmatism following corneal grafting appear to be the configuration of the donor button, and the configuration of the recipient bed. One advance in the carving of the recipient bed has been the development of the Barron-Hessburg corneal trephine. This trephine employs a vacuum system for holding a recipient cornea in position while a hand-rotated trephine cuts out a circular section containing the cornea. However, as explained below, the Barron-Hessburg trephine is not suitable for the treatment of donor tissue.
When keratoplasty was originally developed, it was necessary to preserve an entire donor eye. However, with the development of improved preservation techniques, the more recent development has been to preserve only the corneal-scleral tissue (referred to hereinafter as the donor corneal-scleral button). The Barron-Hessburg technique, while possibly suitable for trephining a donor button from an entire donor eye, is not at all suitable for trephining a donor button from a donor corneal-scleral button.
The standard technique for trephining a donor button from a donor corneal-scleral button is to use a trephine which is positioned over a Teflon block. The trephine is brought down on the corneal-scleral button and a donor button is punched out onto the Teflon block. It has been observed that donor buttons punched out in this way demonstrate an elliptical rather than a round shape. This elliptical shape is accentuated if the punching trephine is not extremely sharp. When such an elliptical donor button is placed into a round recipient bed, tissue disparities and distortions result which sometimes become apparent only following suture removal.
In order to avoid the astigmatism which results from these disparities, a need exists for a system which will eliminate or minimize these disparities which occur between the donor button and the recipient cornea bed.